Increase in wildfires blamed on warming

Matt Weiser

Friday, July 7, 2006 | 7:22 a.m.

SACRAMENTO - American forests in the West have burned bigger and more frequently since 1987, and climate change is a big reason why.

That is the conclusion of a research paper published this week by Sciencexpress.org, the online version of the journal Science. It is the first to document a link between global warming and increased fire intensity in Western U.S. forests.

The study doesn't address what causes fires or firefighting effectiveness. But it finds that climate change creates longer, drier seasons and better conditions for catastrophic fires.

Anthony Westerling, a climatologist at the Scripps Institution of Oceanography at the University of California-San Diego, and his coauthors found a four-fold increase in large wildfires between 1987 and 2003 compared to the preceding 16 years.

The increase corresponds to an average 1.5-degree Fahrenheit temperature rise across the region, which includes the Rocky Mountains, the Southwest, the Sierra Nevada and the Northwest.

During the warmer period, fires burned six-and-a-half times more land area, and the fire season grew by an average of 78 days. The average fire duration also increased, from 7.8 days to 37 days.

"The real message of the paper is not as much about forest management," said Steven Running, a University of Montana ecology professor who was one of the study's peer reviewers. "It's that this is yet another dimension of global warming's impact. To me, it's the equivalent of the hurricanes on the Gulf Coast. This is our hurricane."

As Running spoke in a telephone interview, he was watching firefighting aircraft battle a wildland blaze on the edge of Missoula, only a mile from his office.

In California, officials predict an "average" fire season this summer. Several fires were burning in the state's northern mountains this week, including two near Susanville northwest of Reno totaling 6,000 acres, and another pair totaling about 2,000 acres in the Modoc National Forest.

Containment was expected today on two fires in Southern Nevada, according to wire service accounts. Officials said the Gass Complex fire in the Desert National Wildlife Refuge about 25 miles north of Las Vegas was 60 percent contained on Thursday. Firefighters also continued battling the Mid-Valley fire at the Nevada Test Site on Thursday.

Westerling, who started a new job this week at UC Merced's Sierra Nevada Research Institute, documented the link between fires and climate change after assembling a database of more than 1,100 Western wildfires, plus climate data such as precipitation and snowmelt.

The increased fire activity is partly a result of reduced winter precipitation, earlier snowmelt and a resulting early start to the dry season - all linked to warmer temperatures, he said.

"I think it's really clear that it's climate," said Westerling. "When you look at the timing of these larger fire years in the Sierra Nevada, they're very strongly correlated with the timing of spring and temperature changes."

His co-authors in the study are Hugo Hidalgo and Dan Cayan of the Scripps Institution, and Tom Swetnam of the University of Arizona.

There is broad agreement among scientists that the Earth's climate is warming, and that people's habits are partly to blame. Burning fossil fuels such as gasoline and coal releases carbon dioxide that had been trapped in the ground. This changes the atmosphere, causing more heat to be trapped.

Forest managers in different regions should respond to climate change differently, Westerling said, because people have influenced forests in different ways.

The Sierra Nevada historically had sparse forests and smaller, more frequent fires.

During the Gold Rush of the late 1800s, many Sierra forests were completely cleared to supply wood for mines, railroads and fast-growing cities.

A century of determined fire suppression followed, allowing flammable brush and small trees to accumulate on the forest floor.

Westerling said forest thinning can be helpful in avoiding big fires in the Sierra. But in the Rockies, where forests retain more of their natural structure, thinning projects are less effective.

"There are lots of areas in the Southwest or parts of the Sierra Nevada where fuels management is still a very important policy to pursue," he said.

Matt Mathes, a spokesman for the U.S. Forest Service, said the study's findings don't bode well.

The Forest Service uses fire and cutting on about 100,000 acres statewide every year to reduce fire risk. This includes a controlled burn the agency started on June 23 in the Marble Mountain Wilderness of the Klamath National Forest. It will eventually cover 1,200 acres, a sliver of the 20 million acres the agency manages in California.

Forests are increasingly being viewed as a way to solve global warming, because as trees grow, they take carbon dioxide out of the atmosphere.

But in a companion commentary also published today, Running writes that the Intergovernmental Panel on Climate Change, the leading authority on global warming, predicts a temperature increase for western North America from 3.6 to 9 degrees Fahrenheit between 2040 and 2069.

This could mean the problem documented by Westerling could worsen, Running said, turning forests into a cause of global warming, rather than a solution.